1. Field of the Invention
This invention relates generally to circuit breakers and, more particularly to circuit breakers including a magnetic trip mechanism.
2. Background Information
Circuit breakers having an operating mechanism and a trip mechanism, such as a thermal trip assembly and/or a magnetic trip assembly, are known in the art. An example of such circuit breakers is disclosed in U.S. Pat. No. 5,805,038, which is incorporated by reference herein. The trip mechanism is automatically releasable to effect tripping operations and manually resettable following tripping operations. Such circuit breakers, commonly referred to as miniature circuit breakers, have been in use for many years and their design has been refined to provide an effective, reliable circuit breaker, which can be easily and economically manufactured on a large scale. As such, the ease of manufacture of such circuit breakers is of importance.
Circuit breakers of this type include at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to an operating mechanism. The operating mechanism includes a movable operating handle that extends outside of the housing. The operating handle has essentially three stable positions: on, off, and tripped. The operating mechanism further includes an operating arm, upon which the movable contact is disposed, the trip mechanism, and a cradle. The cradle is coupled to a spring and is disposed between the trip mechanism and the operating arm.
The trip mechanism may include a thermal trip capability, which responds to persistent low level overcurrents, and/or a magnetic trip capability, which responds instantaneously to higher overload currents. One such trip mechanism includes a cantilevered bimetal member, a magnetic yoke and a magnetic armature. The magnetic yoke is a generally U-shaped member secured to the bimetal member at a bight portion of the magnetic yoke with legs thereof facing the armature. The magnetic armature is secured to a supporting spring that is, in turn, secured at its lower end near a free end of the cantilevered bimetal member. Thus, the armature is supported on the bimetal member by the spring. The armature has a window opening through which one of end of the cradle extends. A latch ledge on the cradle engages the edge of the window to latch the latchable operating mechanism in the latched position. The trip mechanism includes three welds: (1) between the bight portion of the magnetic yoke and the bimetal; (2) between the lower end of the bimetal and the lower end of the spring; and (3) between the upper end of the spring and the lower end of the magnetic armature. This assembly procedure is time consuming. Furthermore, the welds are subject to failure.
There is, therefore, a need for a circuit breaker trip assembly, which reduces manufacturing time and/or cost.
There is a further need for a circuit breaker trip assembly, which minimizes a count of welds and/or improves reliability.
There is room for improvement in circuit breakers.
There needs and others are met by the present invention, which provides a single-piece magnetic bracket/armature assembly, and which incorporates the functions of a magnet, an armature having a latching surface, and an armature return spring. The armature and the armature return spring are retained within the confines of the magnetic bracket, in order that the armature performs a trip function resulting from rotational movement. The magnetic bracket may be a formed steel part, which functions as a magnet, while suitably pivotally retaining the armature during operation. The spring may be coupled to the armature and biased to a leg of the magnetic bracket.
In accordance with one aspect of the invention, a circuit breaker comprises separable contacts; an operating mechanism for opening and closing the separable contacts; a conductor electrically connected in series with the separable contacts; a trip mechanism cooperative with the operating mechanism to trip open the separable contacts, the trip mechanism responsive to a predetermined condition of current flowing in the conductor, the trip mechanism comprising: a magnetic member coupled to the conductor, an armature pivotally mounted to the magnetic member, and a spring set apart from the conductor and biasing the armature away from the magnetic member.
The armature may include an opening, and the operating mechanism may include a cradle having a latch surface, which is latched by the armature at about the opening thereof. The spring may include a latch skin, which engages the armature at the opening thereof. The latch surface of the cradle may be latched by the armature at the latch skin of the spring.
The armature may pivot toward the magnetic member responsive to the predetermined condition of current flowing in the conductor, and the armature may responsively unlatch the latch surface of the cradle.
The magnetic member may include a leg coupled to the conductor. The conductor may be a bimetal, which is welded to the leg of the magnetic member.
The armature may include an opening. The magnetic member may include an arm. The spring may include a first portion, which engages the armature at the opening thereof a second portion and a bend portion between the first and second portions, the second portion of the spring flexing and engaging the arm of the magnetic member, thereby biasing the armature away from the magnetic member.
The magnetic member may include a pair of ears having a pair of openings. The armature may include a pair of legs which pivotally engage the magnetic member at the openings of the ears. The ears of the magnetic member may be folded over, in order to capture the armature. The magnetic member may include a generally U-shaped magnetic yoke having a pair of legs facing the armature, with each of the ears being attached to a corresponding one of the legs.
As another aspect of the invention, a circuit breaker comprises: separable contacts; an operating mechanism for opening and closing the separable contacts; a conductor electrically connected in series with the separable contacts; a trip mechanism cooperative with the operating mechanism to trip open the separable contacts, the trip mechanism responsive to a predetermined condition of current flowing in the conductor, the trip mechanism comprising: a magnetic member coupled to the conductor, an armature pivotally mounted to the magnetic member, and a spring set apart from the conductor and biasing the armature away from the magnetic member, the spring coupled to the armature and engaging the magnetic member.
As another aspect of the invention, a circuit breaker comprises: separable contacts; an operating mechanism for opening and closing the separable contacts, the operating mechanism comprising a cradle; and a strip mechanism cooperative with the cradle of the operating mechanism to trip open the separable contacts, the trip mechanism comprising: a bimetal conductor electrically connected in series with the separable contacts, the trip mechanism responsive to a first predetermined condition of current flowing in the bimetal conductor, a magnetic member coupled to the bimetal conductor, an armature pivotally mounted to the magnetic member, the cradle of the operating mechanism latched on and tripped by the armature, the armature and the magnetic member responsive to a second predetermined condition of current flowing in the bimetal conductor, and a spring biasing the armature away from the magnetic member, the spring set apart from the bimetal conductor, coupled to the armature and engaging the magnetic member.
The armature may include an opening. The cradle of the operating mechanism may have a latch surface, which is latched by the armature at about the opening thereof. The armature may pivot toward the magnetic member responsive to the second predetermined condition of current flowing in the bimetal conductor. The armature may responsively unlatch the latch surface of the cradle. The spring may include a latch skin, which engages the armature at the opening thereof. The latch surface of the cradle may be latched by the armature at the latch skin of the spring.